1. Field of the Invention
This invention relates to a catalyst and process for polymerization of olefins. A supported metallocene catalyst is made by treating a support with an alumoxane co-catalyst and complexing a metallocene with the alumoxane. The supported metallocene catalyst is suspended in a diluent. Prior to the introduction into a polymerization reaction zone, the supported metallocene catalyst is contacted with an aluminum alkyl co-catalyst.
2. Description of the Prior Art
Catalysts for the syndiotactic polymerization of olefins are known in the art and have been known at least since U.S. Pat. No. 3,305,538, which described use of a catalyst to produce small quantities of syndiotactic polypropylene which were extracted. Since that time, patents have issued relating to organometallic or metallocene catalysts which produce syndiotactic polyolefins. Examples of these patents include U.S.
Pat. Nos. 4,892,851; 5,132,381; 5,187,250; 5,219,968 and 5,225,507, the disclosures of which, together with the disclosure of U.S. Pat. No. 3,305,538, are hereby incorporated by reference.
These patents disclose metallocene catalysts that are basically a complex derived from a cyclopentadiene, i.e., a metal derivative of cyclopentadiene, which has been ionized by an ionizing agent to form an active cationic metallocene catalyst. It has also become known in the art that metallocenes may be supported on an inert non-reactive material.
In the U.S. Pat. No. 4,701,432 a support is treated with at least one metallocene and at least one non-metallocene transition metal compound. To form a catalyst system a co-catalyst comprising an alumoxane and an organometallic compound of Group IA, IIA, IIB and IIIA is added to the supported metallocene/non-metallocene. The support is a porous solid such as talc or inorganic oxides or resinous materials, preferably an inorganic oxide, such as silica, alumina, silica-alumina, magnesia, titania or zirconia, in finely divided form. By depositing the soluble metallocene on the support material it is converted to a heterogeneous supported catalyst. The transition metal compound, such as TiCl.sub.4, is contacted with the support material prior to, after, simultaneously with or separately from contacting the metallocene with the support.
In U.S. Pat. No. 4,897,455 a metallocene and an alumoxane were reacted in the presence of a support material to provide a supported metallocene-alumoxane reaction product as a catalyst to polymerize olefins, preferably ethylene. The support is a porous solid, such as talc, inorganic oxides and resinous support materials, such as a polyolefin, and is preferably silica, alumina, silica-alumina and mixtures thereof.
In U.S. Pat. No. 4,935,397 a silica gel having a particle size less than 10 microns containing from about 5 to about 20 per cent by weight absorbed water as a catalyst support material. The silica gel is coated with alumoxane and a metallocene is complexed with the alumoxane to form a catalyst which can be used in high pressure and/or high temperature olefin polymerization.
In U.S. Pat. No. 5,200,379 pentadienyl derivatives were complexed with transition metals to form a catalyst which is supported on activated inorganic refractory compounds, preferably inorganic oxides and metal phosphates, such as silica and alumina. The inorganic refractory compounds are activated by calcining in air at elevated temperatures and then contacted with a pentadienyl derivative--transition metal complex, such as bis(2,4-dimethylpentadienyl)titanium. The supported catalyst can be used in olefin, preferably ethylene, polymerization.
In U.S. Pat. No. 5,240,894 a metallocene is activated with methylalumoxane (MAO) to form a reaction product which is contacted with dehydrated silica. After drying, a supported catalyst is formed which can be used in polymerization of olefins, particularly propylene, a trialkylaluminum co-catalyst or scavenger can be used in polymerization to minimize fouling and increase catalyst activity.